Process for straightening rifle-barrel forgings



Jan. 6, 1925. 1,521,717

W. A. sCHMlDT PROCESS FOR ySTRMGH'IENNG RIFLE BARREL FORGINGS Filed Deo. 13, 1918 ATTORNEY.

Patented Jan. 6, i925.,Y '.v

unirse sra-iras WILHELM A. so-rernr, or rLroN, 'New Yoan, essie-Non. :er Massin AssrsNMENrs, rro V` REMINGTON Ari-ras oo'reraNY; rNo.. or New YORK, N.

DELAWARE.

ergens cernes.v

r., a CORPORATION or` rnoonss ron srfaarenrnrirris Birre-BARREL ronsrNGs.

` Application filed December 13, 1918. Serial No. 268,620.

To ZZ whom it may cono/em.'

Be it known that I, WILHELM A. SoHMID'n a citizen of the United Sta-tes, residing at llion. in the county of Herkimer and State of New York, have invented a certain new and useful Improved Process for Straightening Rifle-Barrel Forgingsa of which the following is a specification.V

This invention relates to a process forY straightening rifle barrel foi-gings and for relieving internal stresses and strains from such forgings. y

One object of the invention is to produce a rifle barrel or other similar articleat a lower cost than by methods heretofore used.

Another object is to produce a barrel from which internal strains are practically or entirely absent so that the barrel will notV warp out of true, afteruse as is sometimes the case in barrels made Yby the processes heretofore used.

Other objects are tov improve generally former methods for constructing rifle barrels and other like articles whereby I am enabled to make a better article at a lower cost; u

I attain these Objects by the improved process hereinafter fully described and claimed.

The single sheet of drawings annexed hereto shows an actual stress-strain diagram of a hot steel rod under tension and illustrates graphically the effect of tension on internal stressesand strains.V Y

The manufacture of rifle barrels as here- Atofore practiced was effected substantially as follows: f

VThe rifle barrel forging was formed roughly from heavy round stock' by rolling or forging under a hammer, A large percentage of these forgings were found to be "curved by these operations and needed straightening. This was partially accomplished under a long die while the metal was hot followed by a cold straightening operation before machining. Where cold straightening was necessarythe'bending was necessarily carried far enough to strain the outer fibers beyond the elastic limit. When the bending force was removed those'fibersl theforging certain fibers will be in Vcompression while others are in tension. These strains are irregularly distrlbutedthroughout the metal-but necessarilyA are so disposed on every transverse section that the sum ofl the forces resulting from thev compression strains is equal tothe sum of the forces due to the tension strainsand so disposed relative to each other that theirrespective turning moments aboutV any axis are equal and opposite. This will be the case whether the forging happens to be straight or crooked.

If the forging is not stra-ight it willrequire straightening. The result of this -will be to further increase' the internal strains land to further decrease the homogeneity 4of the metal.'v y

VIt was found that, when forgings made by this old method were maehined the resulting barrel was out of true. TheA removal of the outside metal had destroyed the ydelicate balance of complex internal tension and compression stresses? together' with their corresponding turning moments, so that a readjustment was necessary, one Vresult lof which was the warping ofthe barrel.

It was necessary to stra-ightenthese barreis, but the next machining operation would again destroy the balance of internal stresses and necessitatey further straightening. A-number of alternate-'machining and straightening operations wereV necessary to complete the barrel, but even the finished barrel was straightimerely because the internal stresseshappened to be balanced when the barrel was straight and itfwas found that the many temperature changes,

-ternal strains in the barrel.

vibrations and intermittent stresses incident to the ringof the gun would in time disturb this balanced condition with the result that permanent warping of the barrel took place. 1 Y

It is a fact well known to shooters that if a number of shots are firedfrom sor-.ie rifles as heretofore made, thelater shots are likely to be grouped some distance oif of the target ,and that the sights will have to be reset after a certain number' of shots. The reason for this is that the metal of such barrels is not homogeneous and that there-- fore, the expansion due torheating is not uniform; `For this reason such a barrel may he peigiectlly straight when cold and still be crooked after a few shots.- Y

rAnother well known dillicuity that barrels which ipp-ecui .d to be perfectlyT straight-on final inspection would frequently not shoot Vaccurately Vwhen test-ed in the gailery. The reason for this is not definitely known but the explanation sometimes adH vanc'ed is that the inaccuracy due to inlllhen a high power'rile is shot the barrel is violently whipped rThis whip is a transverse vi bration and throws the barrel into similar to the waves which can be sent along ersely a rope by suddenly moving it trans at one end. lf :a airrel snormally under internal s'resses` these 'waves are irregular or 'of variablewave length or amplitude with tlieresult 1that the shots are unaccountably scattered v Whatever thecause of such erratic results Amay he. it has been found from tests of many thous'andsiof barrels manufactured accordiii`g-to= my present process that reyections froin'such causes have been much reduced.

These many 'ditiiculties have ybeen practically'overcome by my presenti invention.

in my vprocess tl'iefforgings are for-mec. by rolling as formerly. Then immediately after rolling an'dwhi'letl'ie forgingis still ata red heat the lforging is placed in a *stretching machine-and 'elongated slightly .beyond its elasticy limit. VThis stretching operation is performed yin a special machine which formsfth'e vsubJec't of Patent- #7:1567 O99.- Fe' iruary l, i921, but it is evident that vany suitable machine may be `used for this purpose'.

Theeifectof this stretching is two-fold;

*it straightens theforging, but,v what is of Vbreechy end, it 'mi he .necessary to true up the larger portion under a drop hammer. The reaso'iilfor this is. of course that the stress exerted in the larger Section will be `chined and inspected for sti'aightness.

much less than'in the section of smaller a rea and will therefore not exceed the elastic limit. Y

lifter thisthe barrel is alternately mahas been found in practice that a barrel forging which has been treated according to my new process will seldom needstraightening between these machining operations and many of the barrels pass this large number of inspections without requiring single cold straightening.

New we will consider the effect of the 'stretching operation upon the physical con dition of the metal. .The drawing illustra es the actual stress strain curve of a hot forging, the stress being laid off on the line OY while the corresponding strains are laid olf on the line OY.

TWhen thev tensile stress is applied to the barrel the strain is found to be proportional Vto the stress applied, until the elastic liniit is reached, which is in accordance with 'i oolrs law. rl`his`part of the operation is graphically represented by the line OA. lieyoiid the elastic limit strain increases faster thanr the stress as shown by the line All. et the point B the stress strain curve is horizonn tal. ln the use of my process the load and consequently the stress is removed at a point somewhat beyond the elastic limit. it has been found that .in most Vcases the load may be removed at tl, i. e., per cent elontion or that the stretching may be carried somewhat beyond the point B it the fo flu-i fil-10,. l [L\f riferi ing` is at the iwoper temperature. ti limit having been exceeded the i i retains permanent set.

New let us see wl'ia't has happened to those ging' libere which were understress before the y" yresents the -eifectof tensioncn a. liber ner- A to B the curve will beof` the saine shape o as the curve AB.

rlhe line (Y, ifi', represents the effect f tension on fiber normally 1n comprese sion. lt will be noticed that theline il A does not-cross thezero line OX -unlilfthe tensile stress rei resented by the line il t) has Abeen applied Tie elastic linut is reached at and the curve becomes borizontal at B. lt will be noted that the three curves `shown are identical in shape but slightly transposed in a horizontal direction. it `will 'alsobe noted that while there is a considerable. vertical distance between the curvesV below the elastic limit. that this is gradually j decreased and becomes zero where the curves are horizontal. The curve F. Gr shows graphically the rapid decrease of the Vertical distance between the lib? curves and indicates'the rapidity with which difference in stress disappears as the stretching goes on. Until "the elastic limit is reached no decrease takes place and the curve is horizontal for about the first 1/2.% of elongation but then it drops rapidly so that at 1% elongation the difference of stresshas dropped to less than one-eighth of its original value and at the point C' the. difference in stress is only about one-fourteenth ofthe original difference.

It is therefore evident that Whatever the initial condition of any fiber, Whether it be at rest or under more or less tensile or compressive stress, When the forging is stretched to a]'iproximately the point B all fibers will be strained the same distance and ywill bc under the saine stress. Then theload is 'entirely removed all'of 'the fibers are at rest.'

there v are neither compressive Ynor tensile stresses?? All internal stresses have been re- Y lieved and when the forging is subsequently machined, the removal of the metal 'ivillnot disturb the balance of the internal stresses as in forgings Which rhave not been sotreated. If the stress is removed 'before thc pointY B is reached some slight internal stresses may stillv persist but they are too small to be of practical importance and it has been found that very good results are obtained'if the stress is removed at or above approximatelvthe point C. It is of course understood that the stretching operation is carried out when the barrel is at the proper temperature so as not to injuriously affect the physical properties of the metal. The particular temperature suitable for this purpose depends upon the nature of the metal or alloy of the barrel. For steel a dull red heat will give good results. A much lower temperature will be satisfactory for the more ductile metals.

lt will be seen therefore .that I have invented a processs which will at one operation straighten barrel or other forgngs and relieve the internal stresses set up by prior operations, Which taken together with any subsequent machining steps Will produce a barrel notonly quicker and cheaper but also much better in that it will not be inclined to permanently T.varp out of trueas is the case in barrels constructed by any other process. Barrels made by this process Will not tenr poiarilf Warp out of true after a fen shots as so often happens With barrels straight-` ened by bending or without stretching as rcquired by my present process. Another effect7 also referred to above, is that such barrels will shoot more accurately because their vibration Whip is uniform'. l

Another great advantage Which this method of straightening has' resulted in is the high degree of symmetry of mass around the axis throughout the length of the forging which results in obtaining a straighter hole in drilling. This is due to the fact that t-he drilling operation is-perforined by rotating thefoi'ging at a highrate of speed While the drill remains stationary, and owing to the homogeneity of the metal produced by my process there is practically no tendency of the forging to become displaced by bending transversely during the process of drilling as is the case With forgings which ai'e notvbalanced relative to the axis of; rotation, due to centrifugal action Which tends tol result in the drill being forced from vthe center of the barrel during the drilling'operation. Ity has also been found by-actual test that forgings stretched in thisway are somewhat improved in their physical proporties. -Tlie elastic limit and the-percentage of elongation, are somewhat increased.

While I have described my inventionas used in connection with the manufacture of rifle barrels it is of courseobvious` that it is also .applicable to the manufacture of other articles, but probablygall of its func- Jtions Will be` realized lonlyv when used' in manufacturing gun barrels. y l, l

However, Whatl regard s my invention and desire to protect by Letters Patent `of the United States, is:

l. The process' of v producingV straight forgings which consists in first 'rolling the straightening it by 'stretching' the forging .beyond the elastic limit While at a. temperature at which thestretching will not inj uriously affect the physical properties of the metal. v

ings Whici consists in first rolling the forging definitely to shape and then straightening it by. stretching the forging beyond the elastic limit ivhile at a temperature at which' :the stretchingwill not injuriously affect the hammer,.and then straightening the remaining portion by stretching the forging defil' nitely beyond the elastic limit While at a To v Uli

foiging definitelyk to `shape and `then 2. 'The process of producing straight foi'gwv temperature at which the stretching Will notY inliuriously affect the physical properties off.

the metal. v

e. Theprocess of producing straight forgings having an enlarged end Which consists in straightening the enlarged .end portion under a hammer, and straightening the remaining portion by stretching the forging definitely beyond the elastic limit While ata temperature at Which the stretching Will not injuriously affect the physical properties of the metal. n. .V f 5. The process of producing straightv forgings having an enlarged end which consists in i'irstA rolling the forging to shape, straight- Yening the enlarged end portion under a hammer,l and then ,straightening `the remaining portion by stretching the forgingdenitely beyond the elastic limit While at a temperature at Which the stretching Will not injuriously affect thev physical properties of the metal, cooling the forging andY machining it. y

6.- The process of producing straight forgings, having-an enlarged end which consists in straightening Y the enlarged end portion lunder a hammer,r and then straightening the remaining portion by stretching the forging definitely beyondthe elastic limit While at a temperature at which the stretching Will not injuriously -afl'ect the physical properties of the metal,'cooling the forging and machining it.

7; The process of straightening a rifle barrel forging and relieving it of internaly strains which consists in elongating the forgbeyond its elastic limit Whilev hot to a ing t curve is subpoint Where the stress-strain stantially horizontal.

8," The process of straightening a gun bai-- `Vrel forging and relieving Vit of inter-nal strains Which consists in elongatingthe forgingbeyond itsYelastic-'limit While hot to a point Where all fibers Which'ivere normally in compression have been strained to a point VWhere their elongations is continued Without anincrease in total stress.

9.- The process `of straightening a rifle barrel lforging :and relieving itI of internal strains which consists in elongating the forging lbeyond its elasticl limit While hot to a point Where all fibers have been strained to a point Where their elongation is continued Without an increase in total stress.

10. The process of straightening a gun barrel forging and relieving it of internal strains which consists inelongating the forging to a poi-nt beyond its elastic limit and not exceeding the pointwvhere its elongation is continued VWithout an increase in stress. v

l1. The process of straightening a gun barrel forging and relieving it of internal strains which consists in elongating the forging to point definitelybeyond its elastic limit VWhile at a dull red heat.

12. rIfhe process ofstraightening a gun bar-rel forging and relieving it of internal strains' Which consistsin heating tlisforging to a dull red heat and then elongating the forgingbeyond its elastic limit While hot to a point Whereall'libers have been strained to appoint Where their elongation is continued Without an increase intotal stress.

13. The process of vstraightening a riiie barrel forging and relieving of internal strains Which consists in elongati-ng the forging beyond its elastic vlimit While at a dull red heat to a point Where the stress-strain curve is substantially horizontal.

ln testimony whereof I affix my signature.

WILEEDELMy A. SCHMDT. 

